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Cache Consistency and Preservation for Disconnected Systems, Study notes of Mobile Computing

Moradabad Institute of Technology Mobile Computing

The benefits and challenges of caching in disconnected and weakly connected systems, including improved performance and reduced contention on wireless networks. It also introduces solutions for maintaining cache consistency, such as periodic data broadcasting and control information like lock tables or logs. The document further explores coda's file system and its approach to cache preservation through hoarding, emulation, and reintegration states.

Typology: Study notes

2010/2011

Uploaded on 09/04/2011

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Cache Consistency

•Caching is useful during frequent relocation and connection to different

areas.

•alleviate the performance and availability limitations during weak-

connections and disconnections

•reduce contention on the small bandwidth wireless network

•improve query response time, and to support disconnected or weakly

connected operations

•may request different levels of cache consistency Hampered by

disconnection and mobility of clients.

•Solutions:

–Periodically broadcasting the actual data.

–Control information such as lock tables or logs.

Partial preview of the text

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1 Cache Consistency

(^) Caching is useful during frequent relocation and connection to different areas.
(^) alleviate the performance and availability limitations during weak- connections and disconnections
(^) reduce contention on the small bandwidth wireless network
(^) improve query response time, and to support disconnected or weakly connected operations
(^) may request different levels of cache consistency Hampered by disconnection and mobility of clients.
(^) Solutions:
- (^) Periodically broadcasting the actual data.
- (^) Control information such as lock tables or logs.

Cache Preservation for Disconnection

• Coda’s file system allows the cached objects in the

mobile host to be updated without any co-

ordination.

• When it is connected, the system propagates the

modifications and detects update conflicts.

• Coda proposed three states:

(^) Hoarding
- (^) Client cache manager relies on server replication, always on alert for possible disconnection, ensures the critical objects are cached when disconnected.
(^) Emulation (upon disconnection)
- (^) Relies solely on the contents of the cache.
(^) Reintegration (upon reconnection)
- (^) Revalidate all cached objects before use to detect updates at the server.